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The Gas Laws

The Gas Laws. The density of a gas decreases as its temperature increases. Chemical Properties Produce Gases. Chemists harness chemical properties to produce a desired gas through chemical reactions. Such as the reaction of zinc and hydrochloric acid. Physical Properties of Gases.

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The Gas Laws

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  1. The Gas Laws The density of a gas decreases as its temperature increases.

  2. Chemical Properties Produce Gases • Chemists harness chemical properties to produce a desired gas through chemical reactions. Such as the reaction of zinc and hydrochloric acid.

  3. Physical Properties of Gases Gases are compressible and that they assume the shape and volume of any container. Gases are all infinitely soluble in one another. Each of these characteristics can be explained by the distances between the molecules (or atoms) in a gaseous sample.

  4. Physical Properties of Gases are affected by temperature and pressure States of matter simulation.

  5. Collisions of Gas Particles

  6. Kinetic Molecular Theory • explains why gases behave as they do • deals with “ideal” gas particles…

  7. Kinetic Theory

  8. Kinetic Molecular Theory Postulates of the Kinetic Molecular Theory of Gases • Gases consist of tiny particles (atoms or molecules) • These particles are so small, compared with the distances between them, that the volume (size) of the individual particles can be assumed to be negligible (zero). • 3. The particles are in constant random motion, colliding with the walls of the container. These collisions with the walls cause the pressure exerted by the gas. • 4. The particles are assumed not to attract or to repel each other. • 5. The average kinetic energy of the gas particles is directly proportional to the Kelvin temperature of the gas.

  9. Kinetic Molecular Theory Evidence Postulates

  10. Newton’s First Law of Motion (Law of Inertia) Object at rest tends to stay at rest, and object in motion tends to stay in motion at constant velocity unless object is acted upon by an unbalanced, external force.

  11. Elastic vs. Inelastic Collisions 8 3

  12. 8 8 Elastic vs. Inelastic Collisions POW v1 v2 elastic collision v3 v4 inelastic collision

  13. 8 8 Elastic Collision v1 before v2 after

  14. All collisions must be elastic Take one step per beat of the metronome Container Class stands outside tape box Higher temperature Faster beats of metronome Decreased volume Divide box in half More Moles More students are inside box Mark area of container with tape on ground. Add only a few molecules of inert gas Increase temperature Decrease volume Add more gas Effect of diffusion Effect of effusion (opening size) Model Gas Behavior

  15. Kinetic Molecular Theory • Particles in an ideal gas… • have no volume. • have elastic collisions. • are in constant, random, straight-line motion. • don’t attract or repel each other. • have an avg. KE directly related to Kelvin temperature. Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  16. Real Gases • Particles in a REAL gas… • have their own volume • attract each other • Gas behavior is most ideal… • at low pressures • at high temperatures • in nonpolar atoms/molecules Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  17. Characteristics of Gases Gases expand to fill any container. • random motion, no attraction Gases are fluids (like liquids). • no attraction Gases have very low densities. • no volume = lots of empty space Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  18. Characteristics of Gases • Gases can be compressed. • no volume = lots of empty space • Gases undergo diffusion & effusion. • random motion Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  19. Pressure • Pressure is defined as force divided by the area.

  20. Pressure • The mercury in the inverted tube is pushed upward by the force of atmospheric pressure pushing down on the surface of the mercury in the dish. The height of the mercury in the tube changes with changing atmospheric pressure. Under conditions of standard atmospheric pressure, the height of the mercury in the tube is 760 mm. (1 atm = 760 mm Hg = 760 torr = 1.01325 kPa)

  21. Collisions cause Pressure • The pressure of a gas is caused by the collision of molecules against the sides of the container. The force of the collision against the container can be calculated by Newton’s Second Law of Motion: F=ma. The “F” = force, “m”=mass in kg and “a” is the acceleration in m/s2.

  22. Low Pressure vs. High Pressure inside a System The number of collisions of gas molecules against the wall of the container determines the pressure in the container. Notice the difference in the number of collisions. Figure (a) would have a lower pressure than Figure (b).

  23. Pressure • Is caused by the collisions of molecules with the walls of a container • is equal to force/unit area • SI units = Newton/meter2 = 1 Pascal (Pa) • 1 standard atmosphere = 101,325 Pa • 1 standard atmosphere = 1 atm = • 760 mm Hg = 760 torr

  24. Pressure KEY UNITS AT SEA LEVEL 101.325 kPa (kilopascal) 1 atm 760 mm Hg 760 torr 14.7 psi 1 bar = 100 kPa Sea level Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  25. Measuring Pressure The first device for measuring atmospheric pressure was developed by Evangelista Torricelli during the 17th century. The device was called a “barometer” “We live submerged at the bottom of an ocean of air.” Evangelista Torricelli, circa 1644 • Baro = weight • Meter = measure

  26. Empty space (a vacuum) Hg Weight of the mercury in the column Weight of the atmosphere (atmospheric pressure) Barometer Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 401

  27. Water column (34.0 ft. high or 10.4 m) Barometer • Mercury filled 760 mm = 1 atm • Water filled 10400 mm = 1 atm Atmospheric pressure Mercury column (30.0 in. high or 76 cm) The barometer measures air pressure

  28. Barometers Mount Everest Sea level On top of Mount Everest Sea level

  29. Convert the following: 145 mm Hg into bars 450 psi into kPa 900 mm Hg into torrs 4580 Pa into kPa 5. 25 psi into atm 6. 150 atm into Pa 109 kPa into atm 76.9 mm Hg into bars 98.6 torr into kPa 3 atm into kPa Pressure Practice

  30. 0.19 bars 3102.4 kPa 900 torr 4.58 kPa 1.7 at5m 15199108.32 Pa 0.10 bars 13.14 kPa 303.98 kPa 1.08 atm Answers

  31. K = ºC + 273 Temperature Always use absolute temperature (Kelvin) when working with gases. ºF -459 32 212 ºC -273 0 100 K 0 273 373 Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  32. STP STP 0°C 1 atm Standard Temperature & Pressure 273 K - OR - 101.325 kPa 760 mm Hg Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

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